Recently, in the various electronic apparatus such as mobile telephones and car navigation systems, a light-transmitting touch panel is disposed in front of a display device such as liquid crystal or the like. Further, the number of apparatus which can perform the recognition and the selection of characters and symbols shown in the display device through the touch panel and can change over various functions thereof by manipulating the touch panel by pushing using a finger, a dedicated pen or the like is increased. Under such circumstances, there has been a demand for a touch panel which can be manufactured at a low cost and can be surely manipulated. A conventional touch panel is explained in conjunction with FIG. 2. Here, to facilitate the understanding of the constitution of the touch panel, a size of the touch panel in the thickness direction is expressed in an enlarged manner.
In FIG. 2, light-transmitting upper conductive layer 3 made of Indium-Tin-Oxide or the like is formed on a lower surface of film-like light-transmitting upper substrate 1. On an upper surface of light-transmitting lower substrate 2 made of glass or the like, lower conductive layer 4 substantially equal to upper conductive layer 3 is formed. Further, on an upper surface of lower conductive layer 4, a plurality of dot spacers (not shown in the drawing) are formed at a predetermined interval using an insulating resin. A pair of upper electrodes (not shown in the drawing) is formed on both ends of upper conductive layer 3. A pair of lower electrodes (not shown in the drawing) is formed on both ends of lower conductive layer 4 in the direction orthogonal to the upper electrodes.
Further, with respect to approximately picture-frame-like spacer 5, respective outer peripheries of upper substrate 1 and lower substrate 2 are adhered to each other by adhesive layers 5B, 5C which are formed on upper and lower surfaces of film-like base member 5A by coating. In this manner, the touch panel is constituted in a state that upper conductive layer 3 and lower conductive layer 4 face each other with a predetermined gap there between. Spacer 5 is constituted such that to upper and lower surfaces of film-like base member 5A having a thickness of approximately 50 μm, adhesive layers 5B and 5C having a thickness of approximately 25 μm are applied. The whole thickness of 100 μm of spacer 5 is set to become the gap between upper conductive layer 3 and lower conductive layer 4.
Further, the touch panel having such a constitution is mounted on an electronic apparatus in a state that the touch panel is disposed in front of a liquid crystal display device (LCD) or the like and, at the same time, a pair of upper electrode and lower electrode are connected with an electronic circuit (not shown in the drawing) of the apparatus.
In the above-mentioned constitution, when the user manipulates an upper surface of upper substrate 1 by pushing using his/her finger, the pen or the like while observing a display on an LCD or the like at the back of the touch panel with naked eyes, upper substrate 1 is deflected and upper conductive layer 3 at the pushed portion is brought into contact with lower conductive layer 4. Further, voltages are sequentially applied to upper electrodes and lower electrodes from an electronic circuit, the electronic circuit detects the pushed portion based on the voltage ratio between these electrodes, and performs the change over of various functions of the apparatus.
Here, the touch panel having such constitution is disclosed in JP-A-2003-280821.
When the above-mentioned conventional touch panel is used in an electronic apparatus such as a mobile telephone used outdoors or a car navigation system which is mounted on a front portion of a cabin of an auto mobile, there may arise following drawbacks. Particularly, when the touch panel is used under a high temperature or in an environment where the temperature difference is severely large, due to the thermal expansion or shrinkage generated on upper substrate 1 or lower substrate 2, there exists a possibility that the peeling-off between spacer 5 and upper substrate 1 is generated thus making the manipulation of the touch panel unreliable.